Recently, there has been a vast increase in the need for speed and performance of analog and digital signal processing systems. To ensure performance, data converters employed in these signal processing systems have to meet stringent speed and accuracy requirements. While advances in semiconductor technologies have made production of such devices feasible, efficiently testing converter dynamic performance specifications continues to be a challenge.
Dynamic specifications of data converters are important in high-speed applications such as digital communications, ultrasound imaging, instrumentation, and IF digitization. Indeed, device manufacturers not only want to adequately test devices, they also desire to test devices in a timely fashion with cost-effective tools. References to converters or data converters herein should be understood to include A/D converters, D/A converters, data converters, and signal converters; these terms may be used interchangeably. To test high-speed, state-of-the-art, A/D converters for dynamic specifications high-cost, high-speed Automated Test Equipment (“ATE”) is generally used.
Dynamic specification testing of A/D converters requires a Nyquist rate sinusoidal wave test stimulus having at least three bits or more accuracy than the resolution of a data converter. Fast Fourier Transform (“FFT”) analysis can be performed on captured samples from a data converter using high speed testers to calculate dynamic specifications of converters such as Signal-to-Noise ratio (“SNR”) and Spurious Free Dynamic Range (“SFDR”). For high speed data converters (typically having sampling frequencies of 1 Giga sample per second (“Gsps”) or more), the cost of data converter testers that perform these high speed tests is high due to tester resource requirements.
Various past approaches have been proposed for testing dynamic specifications of data converters. One approach utilized a low-resolution sinusoidal wave passed through a bank of filters to generate a spectrally pure sinusoidal wave used for dynamic specification tests. The FFT of the captured response was then used to calculate the test specifications. This method, however, requires expensive ATE for testing dynamic specifications of high speed devices.
Another past approach uses sophisticated digital signal processing techniques for testing data converters. In this approach, a logic analyzer with custom designed software is used to read digital data directly from a data converter output to perform further processing. For high speed devices, however, there arises a need for synchronized low-jitter clocks running at multi-gigahertz frequencies, and this approach does not account for clock synchronization.
To determine the instantaneous value of the dynamic specifications, another approach uses wavelet transforms to compute the non-idealities. Still another approach uses a built-in-self-test approach with two imprecise sinusoidal waves having spectral dependence to determine the device dynamic performance because high purity sine waves are extremely difficult to generate on chip. For high speed data converters, however, generating such high frequency signals on-chip could result in design and reliability issues.
Most of the above mentioned approaches assume the existence of analog sources that can source analog signals at the Nyquist rate of the maximum sampling frequency for a data converter. As the sampling frequencies of the devices under testing (“DUT”) increase, the costs of testers that can source such a signal increases proportionally.
Accordingly, there is a need for low cost production test approaches to test high speed data converters. It is to the provision of such high speed data converter testing devices, methods, and systems that the embodiments of present invention are directed.